This invention relates to lubricating oil compositions containing a mineral base oil and an oil-soluble polyalkylene oxide compound.
Mineral oil lubricants, such as paraffinic or naphthenic petroleum oils, have been used for most lubricating purposes. However, they have certain disadvantages such as relatively low viscosity indices over varying temperatures and high susceptibility to oxidation.
Synthetic lubricating oils such as those of polyalkylene oxide type have been used as substitutes for mineral oil lubricants in certain area because of their relatively high viscosity indices in comparison with mineral oil lubricants.
Since both mineral oils and polyalkylene oxide oils have their own advantages, it would be desirable to combine them. However, most of the polyalkylene oxides such as polyethylene oxide, polypropylene oxide, copolymers of ethylene oxide and propylene oxide and their ethers or esters have limited solubilities in aliphatic hydrocarbons and thus cannot be mixed with paraffinic or naphthenic lubricating oil bases.
We have found that certain polymeric alkylene oxides containing long chain alkylene oxide moieties are substantially freely soluble in aliphatic hydrocarbon liquids and may be mixed with paraffinic or naphthenic lubricating oil bases to improve their properties such as viscosity indices, load-carrying capacities, anti-oxidative properties, wear resistances and the like.